Home – Home – Jornals – Combustion, Explosion and Shock Waves 2025 number 6

A study of hydrogen oxidation in the presence of sulfur dioxide was conducted in an oscillatory mode. It was found that this process occurs via a degenerate chain mechanism, with sulfur oxide (SO), the primary product of sulfur dioxide conversion, playing a significant role. It was shown that the hydrogen oxidation reaction in the presence of sulfur dioxide in the autoignition region under certain conditions (pressure, temperature, gas mixture composition, contact time) proceeds explosively and is accompanied by light emission. A comparison of experimental data on hydrogen oxidation in the presence of sulfur dioxide with the results of calculations using the proposed model of the process under study revealed good agreement. Based on the calculation results, the effective activation energy of the reaction was determined to be 9 200 J/mol.

The paper presents the results of experimental determination of the flammability concentration limits of methane--air--water vapor, methane--hydrogen--air--water vapor mixtures with a methane to hydrogen volume ratio of 1:2 and 2:1, and carbon monoxide--hydrogen--air--water vapor mixtures with a hydrogen to carbon monoxide volume ratio of 4:1 at an initial temperature of 150 °C and a pressure of 101 kPa. The water vapor content varied in the range of 0 ÷ 60 vol. %. The experiments were conducted in a spherical chamber with a volume of 100 dm3. The presence of mixture ignition and flame propagation were recorded using infrared imaging. The flammability limits of the methane--air--water vapor mixture obtained in the experiments are in agreement with the data available in the literature. The flame propagation mode in hydrogen-containing mixtures near the lower concentration limit was recorded in the form of a spherical flame turning into a toroidal vortex.

The effect of chemical nonequilibrium in the combustion process of a diffusion methane-air flame at moderate pressures and temperatures of the initial reactants on the reduction of nitrogen oxide in reactions known as NO reburn was studied. Based on the detailed mechanism of chemical kinetics of methane oxidation GRI-Mech 3.0, an analysis was performed of the distribution of the main NO-reducing substances (CH, CH₂, CH₃, HCCO) in reburn reactions, as well as the initial substances forming NO in Zeldovich reactions, across the thickness of a diffusion laminar flame based on a numerical solution of the Peters-Kuznetsov system of equations using the thin flame front model (flamlet model). In the flame representation as a chain of isolated ideally mixed reactors distributed across the flame thickness, the NO concentration was estimated using a precise analytical formula representing the rates of reburn reactions in accordance with three detailed kinetic mechanisms: GRI-Mech 3.0, Glarborg, and Miller---Bowman. A comparative assessment of the efficiency of these mechanisms for reducing NO concentration was performed; the maximum reduction was 13.3, 23, and 30.4%, respectively. An assessment of the influence of diffusion showed a change in the relative concentration of NO profiles by no more than 0.06%. It was also shown that, as the chemical equilibrium deviates, reburn reactions gradually begin to occur on the "lean" side of the flame (as fuel radicals diffuse across the stoichiometric boundary), and the region of reburn reactions in terms of the composition of the gas mixture expands more than twofold. The contribution of reburn reactions on the lean side of the flame increases steadily and can reach 56% of the total reburn efficiency, which is of practical significance in systems with a high degree of combustion nonequilibrium. The main contributions to NO reduction on the lean side of the flame are reactions with CH (up to 75% via the GRI-Mech 3.0 mechanism) and reactions with HCCO (up to 80% via the Glarborg mechanism).

The results of a study examining the effect of a weak electric field on a Bunsen burner flame are presented, including the combustion of an aerosol consisting of water microdroplets in an air-methane mixture. Analysis of velocity fields obtained using a PIV system revealed changes in the laminar flame front propagation velocity when exposed to a weak electric field. Moreover, over a significant portion of the combustion front, the laminar front propagation velocity can be considered constant. The existence of an ion wind caused by the drift of negative charge carriers is confirmed. The introduction of water microdroplets into the fuel reduces the charge carrier concentration, indirectly evidenced by the fact that the effect of an electric field on combustion in this case leads to smaller changes in the flow structure ahead of the flame front.

The lower temperature limits for flame propagation of mixtures of oil vapor with oxygen and nitrogen in the presence of liquid oil were determined. Experiments showed that the lower temperature limit differs significantly from that expected for oxygen. One reason for this discrepancy is that, in the presence of an ignition source and a large amount of oxygen in the gas phase, diffusion combustion of the liquid oil film present on the inner surfaces of the vessel can initiate. The flame propagates along this film to the bulk of the oil. As the oil continues to diffuse, a pressure increase significantly exceeds that expected for flame propagation through the gas phase.

The gas-dynamic, kinetic, and energy parameters of detonation in dual-fuel methane-hydrogen systems are presented: a) stoichiometric methane-oxygen and hydrogen-oxygen mixtures in various ratios; b) stoichiometric methane-oxygen mixture with added hydrogen in various ratios; c) stoichiometric hydrogen-oxygen mixture with added methane in various ratios; d) lean hydrogen-oxygen mixture with added methane in various ratios; e) enriched hydrogen-oxygen mixture with added methane in various ratios. The main behavioral patterns of such systems are discussed.

A study was conducted to determine the effect of sample length fixation and mechanical activation of the mixture on the combustion rate and elongation of the samples during synthesis, as well as on the phase composition and morphology of the combustion products in the Ti + C system. After activation for 9 min in an AGO-2 mill with an acceleration of 90g using 9 mm diameter steel balls in air, partial mechanochemical synthesis occurred in the mixture, with the TiC product present in addition to the initial Ti and C components. With activation lasting 9 min, the mixture became pyrophoric and, in some cases, ignited upon removal from the activator drum. After mechanical activation lasting less than 9 min, the combustion rate of the mixture increased and the particle size decreased compared to the combustion rate and particle size of the original mixture. With an increase in activation time in the range of up to 9 min, the amount of impurity gases in the mixture increased, which led to an increase in elongation, and at longer times, to the dispersion of the product samples during synthesis. Fixing the sample length significantly increased their combustion rate, but, like mechanical activation of the mixture, did not affect the phase composition of the synthesis products.

A study was conducted on the macrokinetic combustion of a granulated Zr + 0.5C mixture under nitrogen flow conditions. It was shown that the combustion rate increases nonlinearly with increasing gas flow rate, with the combustion process accompanied by sample shrinkage of up to 26%. Experimental data were analyzed using conductive and convective combustion models. Calculations showed that combustion in a nitrogen flow at gas flow rates exceeding 500 l/h occurs via the convective mechanism. It was established that longitudinal sample shrinkage is due to the presence of a significant amount of zirconium melt during combustion. According to X-ray diffraction analysis, the synthesis products are a mixture of zirconium carbonitrides ZrC_xN_y of variable composition. Chemical analysis of the synthesis products revealed that the degree of nitridation of the granulated mixtures is higher than that of the powder mixtures and increases with increasing nitrogen flow through the sample.

To improve inherent safety and reduce energy consumption in industrial explosives production, the water-soluble compound hexamethylenetetramine is being used to replace the traditionally used insoluble fuel oil in ammonium nitrate-based explosives. This oxidizer and fuel, combined in water, create an intermolecular explosive called an ammonium amine explosive. The effect of pH in the range of 4.0 to 5.8 on the density of this explosive, crosslinking time, microbubble formation, detonation velocity, and water resistance was determined. The studies were conducted using density measurements, a digital viscometer, an optical microscope, detonation velocity tests, and a conductivity meter. The results show that ammonium amine-based explosives prepared at various pH levels form numerous chemically sensitized microbubbles, the average diameter of which decreases as the pH decreases. Lower pH values are associated with higher foaming rates and shorter crosslinking and foaming times. The detonation velocity of ammonium amine-based explosives is 3,500-4,200 m/s, slightly lower than that of conventional emulsion explosives. Furthermore, a comparison of the water resistance of ammonium amine-based explosives with crosslinking times of 1 and 24 hours yields contrasting results. A pH of approximately 5.2 sets the boundary between in-situ mixed and packaged ammonium amine-based explosives. Packaged explosives show significant advantages at pH values above 5.2, while in-situ mixed explosives are more advantageous at lower pH values. These results provide a theoretical basis for improving the performance of this new water-resistant nitrated substance and simplify its industrial application.

Aluminum diboride (AlB₂) microcapsules coated with polyvinylidene difluoride (PVDF), fabricated by a simple rotary evaporation method, were studied. According to the morphology study, PVDF forms an intact outer shell on the surface of each individual AlB₂ particle. Compared with uncoated AlB₂, the AlB₂@PVDF microcapsule has a shorter ignition time, more intense combustion, and faster pressure build-up. At an appropriate PVDF content, the measured heat of combustion is higher than that of the composition with unencapsulated AlB₂, due to a higher heat release efficiency during combustion --- 92.3% (the efficiency of the composition with unencapsulated AlB₂ is 85.2%). Mechanistic study shows that the PVDF decomposition product likely accelerates the oxidation of AlB₂ at several reaction stages, providing higher reactivity of the AlB₂@PVDF microcapsules. The use of AlB₂@PVDF in explosives increases density, detonation velocity, and heat release with good component compatibility, while maintaining acceptable mechanical sensitivity. Therefore, AlB₂@PVDF microcapsules are a promising metallic fuel in composite energetic materials.

Using the molecular dynamics method, numerical experiments were conducted to study the dependence of the melting temperature of various materials (copper, silver, titanium, and silicon carbide) on the nanostructure size. Analysis of the obtained data showed that for all materials, starting from a certain nanostructure size, the melting temperature decreases with decreasing nanostructure size.

The problem of measuring particle size distribution in shock-induced flows is discussed. The design of a mobile holographic system developed by the authors, which implements the method of axial pulse holography, is presented. The system enables the acquisition of holograms with a field of view of approximately 20 mm in diameter and a depth of over 20 mm, and the recording of flows of lead particles ≥3-5 μm in size, moving at velocities up to approximately 2 km/s. Examples of shock-induced flows moving in a vacuum, recorded using the mobile holographic system, are presented. These flows consist of both individual particles 5-100 μm in size and, predominantly, filamentary formations 3-10 μm thick. Methods of analog and digital recording and reconstruction of holograms are discussed, as well as the problem of identifying particles in images reconstructed from recorded holograms.

A new type of ammonium nitrate-based explosive is presented, prepared by replacing diesel fuel with liquid coal fuel (coal atomized in water). Experimental results show that the higher the calorific value of the raw coal, the higher the detonation velocity of the new liquid explosive. For example, with a liquid coal fuel content of approximately 9-12% and a calorific value of 5,500 kcal/kg, the efficiency of the new explosive is relatively stable and achieves improved parameters: velocity equals 2,800-3,000 m/s, brisance increased by approximately 7-10%, and the work performed increased by approximately 8-24% compared to an explosive made from ammonium nitrate and diesel fuel. Minimal changes in the physical and chemical properties were observed during 30-day storage. At the same time, the blast efficiency of this explosive was significantly improved by adding composite additives consisting of a new coal-based fuel, diesel fuel, and an emulsifier. Blast tests under industrial production conditions were conducted at the Heidaigou open pit mine. The test results showed that the new explosive exhibits significantly improved brisance and greater work-producing capacity compared to ammonium nitrate- and diesel-based explosives.

Using the electric contact method, the influence of sample porosity, dispersion, and diameter on the detonation velocity of the individual low-sensitivity explosive triaminotrinitrobenzene (TATB) was studied. Data on the detonation wave front curvature were obtained. The results show that, under identical initiation conditions, the detonation process of TATB is complete after the detonation wave travels a distance equal to 3.5 times the explosive sample diameter and is independent of the porosity, dispersion, and diameter of the samples.

To study the effect of initial ambient pressure on the explosion parameters of thermobaric explosives (HE), static explosion experiments were conducted using trinitrotoluene (TNT) as a reference at both low and high initial ambient pressures. Various grades of thermobaric explosives were tested, and a correlation model was proposed for analyzing the overpressure and momentum of the blast shock wave in different initial environments, taking into account atmospheric pressure. Analysis of the pressure data showed that the general propagation and attenuation characteristics of blast shock waves from TNT and thermobaric explosives are essentially the same at different initial ambient pressures. As the initial ambient pressure decreases, both the shock wave overpressure and momentum decrease. The explosion propagation velocity also decreases with decreasing initial ambient pressure. Furthermore, as the explosive mass increases, the reduction in overpressure and momentum decreases for both thermobaric explosives and TNT, and the difference in the shock wave propagation velocities from these two types of explosives also decreases. A comparison of the correlation model results with experimental data yielded average maximum relative errors of 12.3% for TNT and 8.8% for thermobaric explosives in low-pressure environments relative to the shock wave overpressure. Momentum errors were 12% for TNT and 13.7% for thermobaric explosives. These results demonstrate the high accuracy of the correlation model. This correlation model allows one to determine the shock wave overpressure and momentum of an explosion at various initial ambient pressures, and to estimate the shock wave power generated by thermobaric explosives.

The question of how solid rocket propellants react to fragment impacts remains relevant. Identifying potential mechanisms for propellant propellant reaction to fragment damage is crucial for assessing the safety of solid rocket motors and developing high-energy, low-sensitivity propellants. In this study, a fragment impact experiment on a propellant propellant consisting of glycidyl azide polymer, hexogen, and triethylene glycol dinitrate (GRT) was conducted using a 14.5-mm ballistic gun and a high-speed camera to obtain images of the propellant reaction time history under various ballistic behaviors. Based on the obtained images and measured ballistic data, the relationship between propellant reaction characteristics, the primary reaction mechanisms, and two ballistic limits was analyzed. The results of a 10.0 mm diameter tungsten ball impact on a GRT charge contained in a 3 mm thick cylindrical steel shell show that the threshold reaction velocity corresponds to the ballistic limit of fragment penetration into the shell. Below this ballistic limit, no propellant reaction occurs. In the case of a significant reaction delay caused by the ignition of RDX crystal hot spots rather than ammonium perchlorate particles, the propellant reaction upon complete penetration is combustion. Only when a large number of ammonium perchlorate particles and RDX crystals simultaneously ignite hot spots, and the fragment's initial velocity exceeds the charge's ballistic limit by 2.2 times, can the charge undergo reactions more intense than combustion.

The problem of viscous oxide films, which prevent the full release of energy from boron powder during combustion, was overcome using graphene fluoride (fluorographene). This chemical compound was chosen due to its high fluorine content, low hydrogen content, low surface free energy, and strong thermal conductivity. Graphene fluoride reacts with boron, releasing a large amount of heat and gaseous products during combustion, effectively removing the viscous oxide film, and preventing boron agglomeration. Graphene fluoride was synthesized by shear cutting in an emulsifier, and graphene fluoride-boron composites were fabricated by solvent evaporation. Thermal analysis and heat of combustion tests showed that the prepared thin graphene fluoride layer had an average thickness of 1.56 nm. A composite of 20% graphene fluoride and boron showed a 1.86-fold increase in heat of combustion. Moreover, the addition of 20% graphene fluoride effectively improved the heat release during combustion of boron powder, making it comparable to the heat release during combustion of high-energy composites consisting of metal and boron powders.

The results of numerical modeling of cellular detonation propagation in inhomogeneous gas suspensions of aluminum particles in a hydrogen-air mixture are presented. A physical and mathematical model of hybrid detonation is used, describing chemical reactions within the framework of the given kinetics. The model takes into account homogeneous and heterogeneous reactions with the formation of suboxides or solid aluminum oxide particles, as well as phase transitions (evaporation and decomposition of the oxide) in the reaction products. The model is consistent with known experimental data and the results of thermodynamic calculations of detonation parameters and mixture composition at equilibrium. Flows in channels with transverse gradients and discontinuities in particle concentrations are considered. Various patterns of cellular structures are obtained, allowing us to consider the spatial distribution of particles as a controlling factor in detonation processes.

Experiments show that preheating the shaped charge liner improves its penetrating power. This increase is due to the increased ultimate elongation of the formed shaped charge jet due to thermal softening of its material. The possibility of heating the jet itself in free flight by thermal radiation from a tube located in front of the shaped charge, with heat generation within it caused by a chemical reaction of self-propagating high-temperature fusion, is considered. The characteristics of shaped charge jet heating by thermal radiation are investigated using an analytical solution to a one-dimensional axisymmetric problem of unsteady heat conduction for a uniformly elongating cylindrical rod. It is shown that before plastic breakdown of copper shaped charge jets occurs, they can be radiantly heated in free flight to a temperature that allows for a slight increase in the jet's penetrating power.

Impact tests of 1565 aluminum alloy in the impactor velocity range of 242-653.7 m/s revealed that at a certain impactor velocity (626 m/s), a sharp increase in particle velocity occurs in localized regions of the target. Microstructural studies of the sample revealed traces of localized deformation. Simultaneously, material is ejected from the rear surface of the target. This phenomenon correlates with the stochastic behavior of strain carriers at the mesoscopic scale-the presence of mesoparticle velocity dispersion. To account for the influence of stochasticity on shock wave propagation, a system of equations from the continuum theory of dislocations is used, which includes a dislocation velocity distribution function. It is shown that local attenuation or acceleration of the shock wave is determined by the relationship between velocity dispersion and the flow velocity of the dislocations.